Radio receiver



I 3, 1935. Q AM 2,022,805

RADIORECEIVER Filed Nov. 13, 1933 Patented Dec. 3, 1935 UNITED STATES PATENT OFFICE RADIO RECEIVER Delaware Application November 13, 1933, Serial No. 697,835

9 Claims.

This invention relates to radio receivers and particularly to superheterodyne receivers of the multirange type.

It is well known that the design of any multirange receiver involves the satisfying of various conflicting requirements or, in general, the choice of a preferred compromise between the conflicting design requirements. The problem is particularly difficult when the rigid conditions are imposed that the receiver is to be of the superheterodyne type and that the same intermediate frequency is to be employed for all carrier wave ranges. High efiiciency and satisfactory operation over a plurality of ranges may be attained by the use of plug-in inductances and/or tuning condensers, or by the use of Vernier adjustments to correct for a faulty alinement of the several tuning elements but such arrangements are not advisable in radio receivers that are to be manufactured commercially for general distribution to the public. A receiver for general use should be of the single control type and should have selectivity and sensitivity character:- istics in the broadcast band which are comparable with those of the usual single-range broadcast receivers. The performance in the other ranges, which are usually of higher frequency or shortwave ranges maybe less satisfactory than is possible with receivers designed to receive only the higher frequencies but .the primary use of all receivers is on the broadcast band and it is therefore essential that good reception on that band must not be sacrificed in ex tending the operating range of a receiver to include other frequency ranges.

An object of the present invention is to provide an improved type of superheterodyne receiver for operation over a plurality of frequency ranges. An object is to provide a multirange superheterodyne receiver which has high selectivity ,in the lower frequency ranges and which has a high sensitivity in the higher frequency ranges. A further object is to provide a superheterodyne receiver including a fixed intermediate frequency amplifier and a dual-function stage preceding the intermediate frequency amplifier, the said stage operating as a-tuned carrier wave amplifier during the reception of signals falling within one or more ranges of relatively low carrier frequencies and as a first detector stage during the reception. of signals falling within higher frequency ranges. More specifically, an object of the invention is to provide a superheterodyne receiver including one or more inductances and associated switching systems for adapting the inductances to resonate with sections of a gang tuning condenser over different tuning ranges, a local oscillator including inductances and switches which adapt the oscillator to operate over the different tuning ranges, a pair of cascaded tubes, and a circuit network including switches for associating the tubes with the tuned circuits and the oscillator in such manner that the two tubes operate as a carrier wave amplifier and a first detector in the reception of low frequency signals and as .a first detector and intermediate frequency amplifier in the reception of high frequency signals.

Further specific objects of the invention are to provide a novel form of multirange oscillator network which may be alined with .multirange carrier circuits to produce a constant beat or intermediate frequency for all adjustments of the carrier wave and oscillator circuits.

These and other objects and advantages of the invention will be apparent from the accompanying drawing in which the single figure is a fragmentary circuit diagram of a multirange superheterodyne receiver embodying the invention.

the receiver which are peculiar to the present invention and omits the details of the main intermediate frequency amplifier, the detector, the audio amplifier and the reproducer. The particular construction of these elements may conform to any appropriate or desired design and forms no part of the present invention.

As iLustrated, the input system between the antenna A and the first tube of the receiver includes the inductance 2 in parallel with the tuning condenser C which is preferably one section of a gang condenser. A high frequency inductance :3 in series with a switch S1 is connected across the inductance 2 and, as is well known, the closing of the switch S1 changes the tuning range of the input system to cover a higher band of carrier frequencies. The coupling system to the next tube 4 includes both an intermediate frequency and a lower range carrier frequency impedance in'the output network of the tube I, the intermediate frequency impedance being the primary winding 5 which has a secondary winding 6, and the carrier wave impedance being the inductance -1 which has a tapped connection to the plate of tube I by relatively fixed condenser .8. The inductance 1 is tunable over the low range carrier range by the shunt condenser C which may be and preferably is a section of a gang tuning condenser. The-condenser 8 is ad- The drawing illustrates only those parts of sister 24.

justable to tune the primary winding 5 to the intermediate frequency, and the connection 01'.

condenser 8 to coil I is preferably adjustable.

The low potential (carrier frequency) terminal of the inductance 5 is connected to an appropriate source of plate potential +B, through the isolating resistance 9 and is bypassed to the cathode of tube I for carrier frequencies by the condenser C. The tuned circuit I, C includes the large coupling capacity it for coupling to a similar tuned circuit I, C and, preferably, an additional coupling capacity II is provided between the high potential terminals of these tuned circuits to improve the sensitivity versus frequency characteristic of these tuned circuits.

The secondary 6 of the intermediate frequency coupling system is tuned by the adjustable but relatively fixed condenser I2, and the low potential terminals of the inductances' 6 and 'I" are grounded through the high resistance I3 which is in parallel with. the coupling condenser It); The high potential terminalsof the intermediate frequency; and carrier wave frequency coupling circuits are connected, respectively, to the fixed contacts I4, I5 of the switch contact S2 which is connected to the. control grid of the tube 4. The intermediate frequency circuits I. F. into which tube 4 works may be of the usual or desired design. 7

The circuits associated with the local'oscillator tube It are ofappropriate design for operation 'over a plurality of frequency ranges and include a low frequency coil I! in series with the gang tuning condenser section C and with the padding or lagging capacity which is provided by the relatively large fixed condenser is and the smaller adjustable condenser 19. A coil 20 of lower 'inductance than the coil I'I is in series with a small adjustable condenser 2!, the condenser being shunted by a switch S3 and these serially connected elements form a path in shunt with the elements C, 58 and the elements I'I, I9. A small condenser 22 is shunted across the tuning condenser C for alining the high frequency tuning range of the oscillator with the carrier circuit.

One common terminal of the three parallel paths of the oscillatory network is grounded and the other is connected to the grid G of tube I6 through the blocking condenser 23, the grid bias being obtained through the usual grid re- With the switch S3 open the oscillator may be alined for tuning over the low frequency range. The inductance of the coil I'I is'somewhat less than that of the carrier circuit coils 2, l and I and adjustment of the condensers IS and 2! permits a single control'of the tuning circuits, by

adjustable to aline the oscillator tuning with that,

of the higher carrier range to obtain the same constant intermediate frequency by the single control adjustment of the gang tuning condenser.

The plate feedback coupling is obtained through the tickler coil 25 and from the potential drop across the padding condenser I 9 through the coupling condenser 26. The direct' current feed to the plate P is through the resistor 27 which is connected between an appropriate source, indicated as +13, and the'junction of coil 25 and condenser 26. The plate tickler coil 25 is coupled to both the coil I1 and the coil 20, the three coils being conveniently wound on the same form. 5

A coupling coil 28 is connected to one contact 29 of a switch S4 and, through the bias resistor 3i and its shunting condenser 3|, to ground. The other contact 32 of the switch is grounded and the cathode leads 33, 34 of the tubes I and 10 4, respectively, are so connected to the four contacts of the switch that one cathode circuit is returned directly to ground while the other is connected to ground through the coupling coil of the local oscillator. Each cathode lead in '15 cludes a bias resistor 35 and bypass condenser 36, the resistors being of such magnitude as to furnish an automatic bias suitable for operation of the associated tube as an amplifier, and the additional bias necessary for operation of either 20 tube as an efiicient first detector is furnished by the potential drop across the resistor in the coupling circuit. 7

As illustrated in the drawing, the several switches are adjusted for the reception of sig- 25 nals in the lower frequency band. The switches S1 and S3 are open to permit the simultaneous tuning of the input circuit of tube I and the oscillator circuit over their lower range, the switch S2 couples the grid of tube d to the tuned car- 30 rier circuit I, C and the switch S4 is positioned to a ground the cathode circuit of tube I 'and to introduce the local oscillator voltage into'the cathode circuit of the tube 4; The tube 4 operates as the first detector and the three tuned carrier circults preceding this tube provide adequate selectivity for the reception of signals in the broadcast range of from 550 to 1500 kilocycles. For operation over the higher range, the switches S2 and S4 are adjusted to their alternative positions, and the switches S1 and S3 are closed to adjust the inductances of the'respective associated circuits for tuning over the higher frequency range. V

For greater clearness of illustration, the several switches S1, S2, 'etc., are shown as separate elements adjacent the particular portions of the circuits which they control but it will be understoodthat a common operating'member will be provided to control the several switches simultaneously.

The tube I now functions asthe first detector since the local oscillator voltage is introduced into the cathode circuit of that tube while the cathode circuit of tube 4 is returned to ground. The single tuned circuit preceding the tube I provides adequate selectivity in the higher frequency range, and high sensitivity is obtained by the ad- 7 dition of one stage to the intermediate frequency amplifier.

Additional tuning ranges may be provided in either or both of the two general circuit arrangements that are controlled by the adus'tment' of the switch S4. 7

I claim: f

1. In a radio receiver adapted to tune, continu 75.

ously overa plurality of frequency ranges, the combination-with a tube, an input circuit for said tube, said circuit comprising a plurality of inductances and switch means cooperating with a condenser; adjustable to tune said circuit over a plurality of frequency ranges, and a second tube, of a coupling network between said tubes, said network including circuit elements comprisingtwo independent and electrically parallel paths for transmitting high frequency currents of substantially different ranges, one of said paths consisting of relatively fixed circuit elementsand the other path including a circuit tunable over one of the said frequency ranges, and switch means for alternatively rendering one transmission path operative and the other inoperative in accordance with the adjustment of said tuned input circuit for operation over a particular frequency range.

2. In a superheterodyne receiver, the combination with a plurality of cascaded circuits simultaneously tunable over a relatively low frequency range, means adjusting one of said circuits for tuning over a higher frequency range, a tube succeeding the multirange tunable circuit in the direction of transmission through the receiver, a second tube having an output circuit tuned to a fixed intermediate frequency, an intermediate frequency coupling circuit adapted to serve as a coupling between said tubes, an oscillator tunable simultaneously with said multirange tunable circuit to produce an oscillator voltage differing by the said fixed frequency from the resonant frequency of the multirange tunable circuit, and circuit elements including switch means for completing a transmission circuit including both tubes and all of said cascaded tunable circuits or alternatively for completing a second transmission circuit including said multirange tunable circuit and said intermediate frequency coupling circuit between said tubes, said switch means and circuit elements coupling said local oscillator to said second tube when the first transmission circuit is established and coupling said local oscillator to the first tube when the second transmission circuit is established.

3. In a superheterodyne radio receiver, the combination with a tube having an input circuit tunable over a plurality of carrier frequency ranges, of a second tube having an output circuit tuned to an intermediate frequency, and a local oscillator including a network tunable over a plurality of frequency ranges, of means for alternatively introducing the local oscillator voltage into a circuit of one or the other of said tubes, a coupling network between said tubes including circuit elements forming a pair of transmission paths for passing substantially different frequency ranges, and means for alternatively rendering one of said paths operative and the second path inoperative in accordance with selection of the tube upon which the local oscillator voltage is impressed.

4. A superheterodyne receiver of the multirange type comprising a pair of tubes serially arranged in the direction of transmission through the receiver, an input circuit for the first of said tubes and including means for tuning the same over a plurality of frequency ranges, an intermediate frequency output circuit for the second tube,

a local oscillator tunable over a plurality of frequency ranges to produce the same constant intermediate frequency when the oscillator voltage is combined with the desired signal voltage of any of said ranges, a plurality of alternatively operable coupling circuitsbetween said tubes, one ofsaid coupling circuits being tuned. toithe same intermediate frequencyas. that of the output circuit ofithe second tube .and another of said cou pling: circuits 'beingtunable over one of the fre- 5 quency ranges of I the said input circuit; and means for introducing the oscillator voltageinto the second tube and simultaneously coupling said tubes by a tunablecoupling circuit, whereby the first tube operates as .a carrier wave amplifier working intothe second tube, or alternatively introducing the oscillator voltage intothe first tube and coupling said tubes by said intermediate frequencycoupling circuit, whereby the second tube operates .as an intermediate frequency amplifier working-out of said first tube.

5. In a superheterodyne receiver, the combination with a carrier frequency circuit and an oscillator network each tunable over a plurality of frequencyranges 'to produce the sameconstant intermediate frequency for all carrier frequency ranges,. an oscillator tubeconnected to said oscillator network, a pairof :tubes serially arranged in the line of signal transmission through the receiver, said carrier frequency circuit being the input circuit of the first tube, and an intermediate frequency circuit into which the second of said tubes works, of means including switch elements for impressing the oscillatory voltage developed by said oscillator network and tube alternatively upon either of the tubes of said pair, whereby either tube of said pair may be operated as the first detector of the receiver, and means alternatively adjustable to constitute a carrier frequency or an intermediate frequency transmission path between said pair of tubes as, respectively, the second or the first tube of said pair is operated as the first detector.

6. In a superheterodyne receiver, the combination with a first tube having an input circuit tunable over a plurality of carrier frequency ranges, an oscillator having a network tunable simultaneously with said input circuit and over a plurality of frequency ranges to exhibit a constant difference between the oscillator frequency and the resonant frequency of the input circuit, and a second tube having an output circuit tuned to a beat frequency resulting from the combining of the carrier and oscillator voltages, of a coupling network between said tubes and said oscillator; said network including a transmission path tuned to the said beat frequency and a transmission path tunable simultaneously with said input circuit over a lower range of frequency to which said input circuit is tunable, and switch means for introducing the oscillator output voltage into the second tube and coupling said tubes through said tunable transmission path or alternatively introducing the oscillator output voltage into said first tube and coupling said tubes through said beat frequency tranmission path.

'7. In a superheterodyne receiver, a tube having an input circuit including tuning means and a switch for adjusting said circuit for operation over a plurality of frequency ranges, an output network for said tube including a circuit tuned to a fixed intermediate frequency and a circuit tunable simultaneously with said input circuit over the lower frequency range of said input circuit, a second tube, input circuit means for said second tube including a switch for alternatively coupling said tubes through either one of the circuits of said output network, an output circuitfor said second tube tuned to the said intermediate frequency, an oscillator having a nettaneously with the tuning of said input circuit to produce an oscillator voltage that may be combined with the desired carrier voltage to produce a beat frequency equal to the said intermediate frequency, and means for introducing the oscillator voltage into a circuit of the second tube when said input circuit is .tuned over a lower frequency range and said tubes are coupled through said tunable circuit of the output network or alternatively for introducing the oscillator voltage into a circuit of said first tube when said input circuit is tuned over a higher frequency range and said tubes are coupled through the fixed intermediate frequency circuit of said output network.

I 8. A receiver as claimed in claim '7, wherein said means for alternatively introducing the oscillator voltage into a circuit of either tube includes means for adjusting the bias voltages on said tubes to alternative values for amplification or alternatively for detection.

'9. In a multirange superheterodyne receiver, the combination with a circuit tunable over a low and a high frequency range by a section of a gang condenser; of an oscillator tube having an oscillatory network tunable over corresponding frequency ranges by another section of the gang condenser; said network including a fixed and an adjustable condenser in series with the said other gang condenser section and an inductance, and a path connected across said serially connected elements at the junction of the fixed condenser and the inductance and the junction of the said other condenser section and the adjustable condenser, said path including a second inductance in series with an adjustable condenser shunted by a shorting switch, said second inductance being of lower value than said first inductance, and an adjustable condenser shunted across the said other condenser section, the said junctions serving as the opposite terminals of the oscillatory network.

' PAUL O. FARNHAM. 

